Dressel, a two-time Olympic gold medalist who specializes in the sprint events, set the record in a semifinal heat with a time of 49.50 seconds — shaving 0.32 seconds off Phelps' mark that he set at the 2009 world championships.

Caeleb Dressel of the United States of America (USA) celebrates a New World Record after competing in the men's 100m Butterfly semifinal during the Swimming events at the Gwangju 2019 FINA World Championships, Gwangju, South Korea.(Photo: YONHAP, EPA-EFE)

The 22-year-old swimmer will be a heavy favorite in Saturday's final, as he was 1.44 seconds ahead of Russia's Andrei Minakov, who had the second-fastest qualifying time.

“Just the standard that Michael set, wanted to go after it,” Dressel told reporters after the heat. “I hope he was happy watching me do that.”

Dressel also holds American records in the 50-meter and 100-meter freestyle and the 50-meter butterfly. He won both his Olympic gold medals at the 2016 Rio Games on relay teams, including one with Phelps on the 4x100-meter freestyle.

The University of Florida graduate is expected to star at the Tokyo Games next summer, having won seven gold medals at the 2017 world championships, only the second American to ever do so -- behind Phelps.

The medals for the Tokyo 2020 Olympic Games are unveiled as Ryohei Miyata, commissioner for cultural affairs and Tokyo 2020 medal design competition panel chairperson, speaks during a ceremony marking one year before the start of the games in Tokyo on July 24, 2019. BEHROUZ MEHRI, AFP/Getty Images

Japanese designer Junichi Kawanishi wrote that the medals are to “resemble rough stones that have been polished and which now shine with light and brilliance," according to the AP. Atsushi Tomura, Getty Images